Patent print DE-A1 3331046 describes a process for treating silicon and ferrosilicon with slag. In this process a silicate smelt with the composition
______________________________________ K.sub.2 O 2 to 13% by weight Na.sub.2 O 0 to 2% by weight .SIGMA. K.sub.2 O + Na.sub.2 O 2 to 13% by weight SiO.sub.2 45 to 72% by weight Al.sub.2 O.sub.3 0 to 30% by weight .SIGMA. SiO.sub.2 + Al.sub.2 O.sub.3 60 to 78% by weight CaO 0 to 30% by weight MgO 0 to 30% by weight .SIGMA. CaO + MgO 15 to 30% by weight CaF.sub.2 0 to 10% by weight MgF.sub.2 0 to 10% by weight .SIGMA. CaF.sub.2 + MgF.sub.2 0 to 10% by weight .SIGMA. CaO + MgO + CaF.sub.2 + MgF.sub.2 15 to 30% by weight ______________________________________
and impurities due to the raw materials, is smelted and overheated in a resistance furnace. Solid, preferably low-grade, dusty silicon or silicon waste is fed into this silicate smelt. At the end of the melt-down or refining process the silicon is tapped. The silicon thus obtained can be processed like lumpy silicon produced by smelting metallurgy.
This process works by batch processing. This has the disadvantage that the furnace charge comprising slag and melted-down silicon must be greatly overheated before tapping so that a high yield of silicon can be obtained. Unless previously overheated the furnace cools down during the following charging of silicon or silicon dust to such an extent that silicon dust slags and yield is lost or the melt-down slag becomes useless prematurely.
A further disadvantage of this process is that from tap to tap the discharge must be burned out. This detracts from smelting time. Pour-out time is also lost for the melt-down process. A further time loss is caused by the charging of the silicon or silicon dust. Cooling of the slag by the cold silicon reduces the furnace efficiency by up to one half for a period of about 1/4 hour to 1/2 hour.
When liquid silicon is not smelted from silicon dust or waste silicon but produced by the customary carbothermic reduction process it must be subjected after tapping to an elaborate refining process in a ladle to obtain the necessary purity of so-called chemical qualities. In the refining processes currently employed here, oxygen or oxygen/nitrogen mixtures are top-blown onto the silicon in the tapping receiver or blown through the silicon smelt to oxidize aluminum and calcium. The resulting losses due to combustion, slagging and splashing are up to 15% of the weight of the tapped silicon. After being refined the silicon is poured into tubs like the silicon melted-down from dust or waste.
For carrying off the resulting large silicon plates or the tundish filled with silicon to the crushing plant one requires heavy loading machines or high-lift trucks. For coarse-crushing the silicon plates or blocks, which are up to 500 mm thick, one requires several large crushers arranged in tandem. The processing of the large-sized silicon is thus very costly and labor-intensive.
Laid-open print DE 36 10 257 describes a process for granulating slags and molten baths such as silicon to obtain foamed slag or granular material as large-sized as possible. This process is problematic for producing granular silicon since hydrogen explosions can occur as soon as the ratio of the amount of poured-in silicon to the amount of water used is not right or the temperature of the poured-in silicon is too high. Large amounts of hydrogen then develop immediately, involving the danger of an oxyhydrogen explosion.
The invention is based on the problem of providing a continuous process for smelting and/or refining and for continuously pouring and coarse-crushing silicon which avoids the disadvantages of the prior art, and an apparatus for carrying out this process.